The present invention relates to the deactivation of microorganisms, and more particularly to the deactivation of microorganisms using short-duration, high-intensity pulses of broad-spectrum polychromatic light. Even more particularly, the present invention relates to the deactivation of microorganisms in food products, packaging, materials, medical instruments and the like using such pulses of light.
Substantial technical effort has been directed to extending the storage time for foodstuffs and other microbiologically labile products and to preserve these products against microbiological spoilage. Such efforts have involved both the treatment of products and the development of packaging techniques for preservation.
A particular need which exists for methods and apparatuses for sterilizing or reducing the microbiological burden on the surfaces of or within food products, packaging materials, medical instruments, and other products. Such methods and apparatuses may be utilized to reduce or eliminate the need for chemical preservatives. For example, baked goods such as bread may accumulate microorganisms, such as mold spores, from the air after they are baked but before they cool sufficiently to be packaged. Any substantial reheating of the baked goods would excessively dry such goods. Thus, new methods for surface sterilization of such food products, not involving the reheating of such food products, are desirable.
Food products may also be subject to enzymatic degradation, which limits shelf life of the food product. Enzymatic degradation is particularly rapid and evident for example in the browning of freshly cut potatoes and apples, but has adverse effects in a great variety of foods. Enzymatic degradation may act alone, or in combination with microbially caused deterioration.
One example of a food product for which methods and apparatuses for deactivating microorganisms is needed is fresh fish. Fresh fish has a relatively limited storage time before being subject to microbial and/or enzymatic spoilage, which limits the distribution and marketing of fresh fish products. Methods and apparatuses suitable for extending the shelf life of perishable foods such as fresh fish, poultry, beef and pork are highly desirable.
Also, many products, for example some juices, are now processed through the use of heat under conditions that, in order to produce the desired reduction in biological activity, cause a degradation of the taste and palatability of the treated food product. Methods and apparatuses for reducing or eliminating biological activity without such degradative heating are desirable for providing taste and palatability benefits that increase consumer interest and, thus, market for food products so treated.
Significant research and development effort has recently been directed to aseptic packaging technology for packaging of sterilized food products (including high and low acid foods) in sterile packaging materials, in order to provide preserved food products having an extended shelf life. However, such methods and apparatuses may have various disadvantages such as requiring the extensive use of chemical disinfectants which may leave residual chemical products on the packaging material or foodstuff. New methods and apparatuses for sterilizing food product packaging material and for aseptic packaging are desirable.
One example of an aseptic packaging system in combination with a photobiological food treatment apparatus is shown in U.S. Pat. No. 4,871,559, issued to Dunn et al., for METHODS FOR PRESERVATION OF FOODSTUFFS, issued Oct. 3, 1989, and incorporated herein by reference. Short pulses of incoherent, broad spectrum light are used to preserve food products against microbial degradative processes. As a result, the teachings of the '559 patent provide significant shelf-life and stability enhancements to the food product. Application of pulses of high-intensity, incoherent polychromatic light provides efficient, effective, high throughput processing and results in many practical and economic advantages. Moreover, the short duration and the spectral range of each pulse permits spatial localization of various of the preservative effects of the light pulses to a thin surface layer such as the surface of the food product or packaging material.
Fresh fruits, vegetables, and other food products, for example, strawberries, accumulate microorganisms, which as used herein includes bacteria, viruses, and fungi, from the air, ground, water and other sources with which they come into contact. These microorganisms, through various known mechanisms, cause the perishable food products to spoil, thereby significantly limiting the shelf-life of the food products. (Shelf-life is the period of time during which the perishable food product can be stored refrigerated or unrefrigerated, and remain edible and free from noticeable or harmful degradation or contamination by microorganisms.) As a result, methods and apparatuses suitable for deactivating, i.e., killing or sterilizing, such microorganisms and thereby extending the shelf-life of perishable foods, such as strawberries, oranges, tomatoes, zucchini, apples, and other edible food products, are desirable.
The photobiological effects of light, including infrared light (780 nm to 2600 nm; i.e., 3.9.times.10.sup.14 Hz to 1.2.times.10.sup.14 Hz), visible light (380 to 780 nm; i.e., 7.9.times.10.sup.14 Hz to 3.9.times.10.sup.14 Hz), near ultraviolet light (300 to 380 nm; i.e., 1.0.times.10.sup.15 Hz to 7.9.times.10.sup.14 Hz) and far ultraviolet light (170 to 300 nm; i.e., 1.8.times.10.sup.15 Hz to 1.0.times.10.sup.15 Hz), have been studied, and efforts have been made to employ light to deactivate microorganisms on food products or containers for food products. See, e.g., U.S. Pat. Nos. 4,871,559; 4,910,942; and 5,034,235, issued to Dunn et al. (hereinafter, the '559, '942, and '235 patents, respectively), all of which are incorporated herein by reference.
Other studies of the photobiological effects of light are reported in Jagger, J., "Introduction to Research in Ultraviolet Photobiology", Prentice Hall, Inc., 1967. U.S. Pat. No. 2,072,417 describes illuminating substances, e.g., milk, with active rays, such as ultraviolet rays; U.S. Pat. No. 3,817,703 describes sterilization of light-transmissive material using pulsed laser light; and U.S. Pat. No. 3,941,670 describes a method of sterilizing materials, including foodstuffs, by exposing the materials to laser illumination to inactivate microorganisms.
Another attempt to prolong the shelf-life of perishable food products consists of the application of microbiocides and/or microbiostats to the surface of the perishable food products. As used herein, the terms microbiocide and microbiostat include substances for killing or preventing the growth/reproduction of microorganisms (as the term microorganisms is defined herein). One example of microbiocides are chemical fungicides. Generally, the microbiocide and/or microbiostat is combined with an emulsifying agent and is then applied to the surface of the food product. The emulsifying agent aids in the application and action of the microbiocide and/or microbiostat agent, and ensures that the microbiocide and/or microbiostat agent remains on the surface of the food product and deactivates microorganisms during shipping until the food product is consumed.
Problematically, such microbiocides and microbiostats have come under increased scrutiny by various governmental agencies, and in some cases have been shown to be potential human carcinogens. As a result, several microbiocides and microbiostats that were once commonly applied to the surface of food products in order to prolong the shelf-life of the food products have been or could be banned by governmental agencies from use with food products. Therefore, an approach to prolonging the shelf-life of perishable food products, that does not require the use of a microbiocide or a microbiostat, such as a chemical fungicide, is highly desirable.
The present invention advantageously addresses the above and other needs.